Study On The Nitrogen Loss In The Protected Soil Under Different Water And Nitrogen Conditions During Cucumber Growing Season

With the human demand of vegetables increased, farmers ignore the scientific concept of water and fertilizer management. In order to obtain high-yield of vegetable, the amount of fertilizer and irrigation water is improved blindly. Up to now, the problems of soil environment deterioration, low fertilizer use efficiency and worse vegetables quality are very serious. They are all caused by the unreasonable management of water and fertilizer in vegetable production. The way of nitrogen loss and also scientific management of water and fertilizer should be defined in vegetable production. These are urgent for sustaining development of facility agriculture. Up to date, there have few researches on comprehensive and systematic study about the ammonia volatilization, de-nitrification, N2O emissions and the leaching loss of inorganic nitrogen. Field plot experiments and micro-plot experiments of 15N tracing were established in Xinji City, Hebei Province. Our experiment included six treatments both in field trail and micro-plot experiment with 15N tracing to compare the study on reduction of irrigation, nitrogen and conventional of water and nitrogen treatments: (1) conventional water application and with no nitrogen applied (irrigation amount, 7470 m3·hm-2); (2) conventional water application and with nitrogen decreased by 25% applied (irrigation amount, 7470 m3·hm-2; amount of nitrogen, 900 kg·hm-2); (3) conventional water and nitrogen application (irrigation amount, 7470 m3·hm-2; amount of nitrogen, 1200 kg·hm-2); (4) water decreased by 30%, nitrogen decreased by 50% applied (irrigation amount, 5190 m3·hm-2; amount of nitrogen, 600 kg·hm-2); (5) water decreased by 30%, nitrogen decreased by 25% applied (irrigation amount, 5190 m3·hm-2; amount of nitrogen, 900 kg·hm-2); (6) water decreased by 30%, conventional nitrogen application, (irrigation amount, 5190 m3·hm-2; amount of nitrogen, 1200 kg·hm-2). We studied the effects of different amount of water and nitrogen on the field ammonia volatilization, denitrification, N2O emissions, and the leaching loss of nitrate nitrogen and also the fate of 15N and cucumber quality in this research. In our experiment, the main results were as follows:1. During the cucumber growing season, ammonia volatilization content of the field was 11.4~26.6 kg·hm-2 and the loss ratio of nitrogen was 0.89%~1.27% and the contribution rate of nitrogen was 31.8%~57.1%. The ammonia volatilization contents of the treatment with W2N900 and W2N600 decreased by 22.1%, 37.2% respectively under the reduction of irrigation water conditions. Compared with conventional water applied (W2N1200), the ammonia volatilization content of reduction water treatment increased by 3.0%~4.8% with the same nitrogen conditions.2. The gross nitrification rates and denitrification rates of field were 523μg N·kg-2·h-1,351μg N·kg-2·h-1 respectively. The gross nitrification rates of the treatment with W2N900 and W2N600 decreased by 19.9%, 26.7% respectively and the denitrification rates decreased by 9.8% and 20.8% under the reduction of irrigation water conditions. The gross nitrification rates and denitrification rates decreased by 2.5%~11.5%, 19.5%~26.0% respectively in the treatment of reduction water compared to conventional water (W2N1200) under the same nitrogen conditions.3. The N2O loss amount of field was 0.74~7.92 kg·hm-2, and the loss ratio of nitrogen was 0.25%~0.60%, the contribution rate of nitrogen was 67.8%~90.6%. The N2O loss amount of the treatment with W2N900 and W2N600 decreased by 39.9%, 54.1% respectively under the reduction of irrigation water conditions. The treatment with reduction of water compared to conventional water, the N2O loss amount decreased by 36.8%~45.2% under the same nitrogen conditions.4. Inorganic nitrogen leaching amount was 120~595 kg·hm-2, account for 25.6%~39.6% of nitrogen applied. Nitrate nitrogen was the main form of the leaching loss of inorganic nitrogen, and the ratio was 99.7%. The nitrate nitrogen leaching amount of the treatments with W2N900 and W2N600 decreased by 30.3%, 46.0% respectively under the reduction of irrigation water conditions. The treatment with reduction of water compared to conventional water, the nitrate nitrogen leaching amount decreased by 14.9%~23.8% under the same nitrogen conditions.5. Compared with W2N1200, the yield of treatment W2N900 and W2N600 increased by 4.6%, 5.4% respectively under the reduction of irrigation water conditions. Compared with W1N900, the cucumber yield of W2N900 increased by 3.4% under the same of nitrogen applied.6. The effects of different water and nitrogen on quality were significantly. Compared with W2N1200, the NO3- amount of cucumber in the treatment W2N900 and W2N600 decreased by 9.8%, 13.5% respectively, and soluble sugar increased by 13.1%, 12.9% respectively under the reduction of irrigation water conditions. Compared with W1N900, the amount of NO3- in the treatment W2N900 decreased by 3.9%, while soluble sugar increased by 7.3%.7. The effects of different water and nitrogen conditions on WUE were significantly. Compared with W2N1200, the water use efficiency of treatment W2N600 decreased by 1.2%~9.8% with the reduction of irrigation water conditions. Compared with W1N900, the water use efficiency of treatment W2N900 decreased by 6.1% with the same amount of nitrogen applied.8. Micro-plot experiment with 15N tracing showed that absorbed of nitrogenous fertilizer 15N by cucumber was 177~297 kg·hm-2. The amount of absorption by fruit, leaf, stem, and root were reducing in turn. Nitrogen use efficiency was 23.6%~32.8%. The treatments W2N900 and W2N600 had the highest nitrogen use efficiency. Compared with the treatment W1N1200 and W2N1200, they increased by 4.57, 6.96 percentage respectively.In conclusion, the treatments W2N900 and W2N600 were much more reasonable management approach. Because they not only had the higher growth characteristics, water and nitrogen use efficiency, but also with the higher cucumber yield and quality. Two years experiment showed that the water decreased by 30% and nitrogen decreased by 25%~50% would not affect the yield of cucumber. So we recommended that the water irrigate amount was 5190 m3·hm-2, and the amount of nitrogen was 600~900 kg·hm-2 in this area.